1. FIELD OF THE INVENTION
This invention relates to the production of alkali metal silicates and more particularly to a unique process for producing alkali metal polysilicates having a high bulk density and free-flow properties.
2. DESCRIPTION OF THE PRIOR ART
As known in the art, alkali silicates can be manufactured by the so-called "fusion" process wherein a mixture of sand and an alkali metal salt are fused at temperatures sufficiently high to volatilize the acid radical of the salt used. The "glass" thus produced is then cooled and dissolved in water, usually at elevated temperatures and pressures, to yield a product suitable for commercial use. For use in detergents, such silicates are conventionally converted into the hydrated solid form by concentrating the solution, removing the silicates by crystallization and thereafter drying the crystals.
A further known method for producing silicates is the "wet digestion" method wherein a solution of finely divided silica, rendered soluble by digestion with a concentrated solution of caustic alkali, is evaporated and cooled to a suitable crystallization temperature.
Examples of the above and further techniques for producing alkali metal silicates are disclosed in U.S. Pat. Nos. 2,161,515; 2,282,018; 2,357,723 and 3,271,317.
In this regard, and again as is well known in the art, detergent compositions conventionally contain a detergent compound i.e., a surfactant and a "builder", the latter serving in part, to increase the effectiveness of the detergent component. Phosphate compounds, such as sodium tripolyphosphate, have been used somewhat extensively as builders in detergents for many years. However, the use of other inorganic salts including alkali metal silicates, carbonates, borates and the like is, also, known. An example of built detergent compositions disclosing the use of the above noted inorganic materials is disclosed in U.S. Pat. No. 3,392,121 which issued July 9, 1968 to Gedge.
While the use of silicates as builders is known as indicated above, commercially available products do not, in general, have properties, e.g., density, moisture content, etc., such that they may be used as a direct replacement for polyphosphates and the like.